So called C-clamps have been in use since ancient times. The usual modern form of the device involves a C-shaped frame, with some form of a bearing pad formed or mounted at one extremity of the frame. The opposite extremity will usually have a clamping rod movably mounted in a direction toward and away from the pad to generate clamping pressure. This rod is often threaded along its entire length, but one known modification has a rapid-traverse arrangement in which the rod is slidably mounted in a collar having threaded engagement with the frame. This form of the unit will have a one-way rotative interlock between the shaft and the threaded collar such that rotation in this direction corresponds to movement of the collar in the thread system to carry the shaft toward the pressure pad.
The C-clamp has been applied to a somewhat different field of use relatively recently. In electrical welding procedures, it is necessary to provide a return path for the current from the piece being welded to the welding generator. This has sometimes been accomplished by simply applying a C-clamp to the welded piece, with a cable terminal entrapped under grip of the C-clamp so that the terminal bears solidly against the welded member. Sometimes the clamp is used to hold a couple of members being welded together, while serving the additional function of securing the cable terminal in position to receive the return current. To facilitate either of these arrangements, there has been occasional use of semi-permanent securing of the cable terminal to the clamp, with a nut engaging a bolt-like projection. This makes a very handy arrangement when the clamp is used exclusively for a welding terminal, but causes too much inconvenience whenever it is desirable to use the clamp for some function unrelated to welding. It is highly desirable to provide quick-disconnect arrangements both with respect to the cable terminal and also with regard to the engagement and disengagement of the clamping mechanism. The rotative interlock previously discussed has shown a tendency to seize to the extent that back-rotation to release clamping pressure generates a corresponding tendency for the threaded sleeve to move to the extremity of its thread system before the rotative interlock is released. This eliminates some of the desirable features of the rapid-traverse disengagement and adjustability.